1. Field of the Invention
This invention relates to oil and gas drilling, and more particularly to apparatus and methods for integrating network and other transmission media into downhole drilling tools.
2. Background
During downhole drilling operations, drilling jars are used to send shock waves up and down the drill string to dislodge or loosen stuck drill string components, such as a drill bit. Most drilling jars operate by storing potential energy generated from tension or compression in the drill string caused by straining or compressing the drill string uphole at the drill rig. The jar releases this potential energy by suddenly opening, thereby allowing energy stored as strain or compression in the drill string to be released, causing shock waves to travel in a desired direction along the drill string. These shock waves may be sufficient to dislodge a stuck downhole tool or tools.
Most downhole tools have several characteristics in common. For example, due to the shape and configuration of a drill string, many downhole tools, with the exception of the drill bit, have a “pin end” and “box end” to enable the tools to be connected in series along the length of the drill string. The pin end is characterized by external threads that may be threaded into corresponding internal threads of the box end. Because torque is applied to the drill string to rotate the drill bit, the box end and pin end are rotationally fixed with respect to one another. In most cases, the box end and pin end are also axially fixed with respect to one another, meaning that the length of the tool is fixed.
However, in certain types of downhole tools, such as in downhole jars, the length of the tool is variable. For example, a downhole drilling jar generates shock waves by allowing rapid axial movement between the box end and pin end. The axial movement is suddenly stopped when an internal “hammer” hits an internal “anvil”, causing significant shock waves to propagate from the jar. In most jars, the total axial range of motion is limited to approximately 24 inches.
As drilling continues to advance, downhole tools that have axial movement between the pin end and box end may present certain challenges. For example, apparatus and methods are currently being developed to integrate network cable or other transmission media into downhole tools in order to transmit data from downhole tools and sensors to the surface for analysis. This may enable information to be transmitted at much higher speeds than is currently available using current technologies, such as mud pulse telemetry.
Most cables use various types of metals, such as copper or aluminum, to transmit electrical signals. These cables are generally fixed in length and are not suitable to be significantly stretched. In axially rigid tools, namely those tools that have a fixed length, integrating cable or other transmission media into the tool body may require little stretching or adjustment of the cable's length. However, in downhole tools such as drilling jars, where the length of the tool may change significantly, apparatus and methods are needed to integrate transmission cable into the tool body, while accommodating changes in the tool's length.
Another problem is the lack of space within the tool to integrate transmission cable. For example, in drilling jars, most of the internal space of the jar is dedicated to components, such as the hammer, anvil, hydraulic fluid, valves, and other moving parts. Thus, apparatus and methods are needed to integrate transmission cable into the tool, while avoiding interference with components inside the tool. Certain types of jars may accommodate the integration of transmission cable better than others depending on their internal structure and functions.